1. Field of the invention
The present invention relates to a piezoelectric resonator device and, more particularly, to an improved arrangement of such a piezoelectric resonator device.
2. Description of the Prior Art
One prior art piezoelectric resonator device is shown in FIGS. 1, 2 and 3. It includes inner casing 4 having a rectangular opening formed therein with four pointed fingers 4a, 4b, 4c and 4d inwardly extending. A base plate 6 made of metal and having a projection 6a is placed under inner casing 4, thereby closing the bottom of the inner casing 4. An anisotropic conduction pliable sheet such as a layer of rubber sheet 7 containing particles of electric conductive elements aligned in its thickness direction of the rubber sheet for permitting electric connection only in its thickness direction is inserted in a space defined by four fingers 4a, 4b, 4c and 4d. A piezoelectric resonator element 3 deposited with opposite electrodes 1 and 2 is installed in inner casing 4, as best shown in FIG. 2. A top plate 5 made of metal and having a spring arm 5a is placed over inner casing 4, thereby closing the top of casing 4. Then, inner casing 4 is inserted in an outer casing 8, as shown in FIG. 3. Thus, piezoelectric resonator element 3 is held between projection 6a and spring arm 5a through rubber sheet 7 at approximately center of element 3 where the node of vibration exists.
An electric connection to piezoelectric resonator element 3 is effected by top plate 5 through rubber sheet 3 and bottom plate 6.
According to the prior art resonator device described above, four fingers 4a, 4b, 4c and 4d are provided to prevent piezoelectric element 3 from being moved side directions, such as shown by arrows A, thereby preventing it from touching the inner wall of inner casing 4. However, when these fingers 4a to 4d touch the piezoelectric element 3, the mechanical quality factor Qm of piezoelectric element 3 becomes poor, thereby deteriorating its impedance characteristic from curve h1 to curve h2, shown in FIG. 4.